x86: adjust xsave structure attributes

The packed attribute was pointlessly used here - there are no
misaligned fields, and hence even if the attribute took effect, it
would at best lead to the compiler generating worse code.

At the same time specify the required alignment of the fpu_sse sub-
structure, such that the various typeof() uses on that field obtain
pointers to properly aligned memory (knowledge which a compiler may
want to make use of).

Also add suitable build-time checks.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index 331a401d0149482937cb2db0a342642d49cd85a6..67016c95eb60207e6a0ff13b8c3344054053ce5c 100644 (file)
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -277,7 +277,9 @@ int vcpu_init_fpu(struct vcpu *v)
     }
     else
     {
-        v->arch.fpu_ctxt = _xzalloc(sizeof(v->arch.xsave_area->fpu_sse), 16);
+        BUILD_BUG_ON(__alignof(v->arch.xsave_area->fpu_sse) < 16);
+        v->arch.fpu_ctxt = _xzalloc(sizeof(v->arch.xsave_area->fpu_sse),
+                                    __alignof(v->arch.xsave_area->fpu_sse));
         if ( v->arch.fpu_ctxt )
         {
             typeof(v->arch.xsave_area->fpu_sse) *fpu_sse = v->arch.fpu_ctxt;

diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index 4e87ab33875518cc0dda865c782c5be7972a0e41..f5d62feefc2327f669d16b9cb48b8e33c4dd30e6 100644 (file)
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -414,7 +414,8 @@ int xstate_alloc_save_area(struct vcpu *v)
     BUG_ON(xsave_cntxt_size < XSTATE_AREA_MIN_SIZE);
 
     /* XSAVE/XRSTOR requires the save area be 64-byte-boundary aligned. */
-    save_area = _xzalloc(xsave_cntxt_size, 64);
+    BUILD_BUG_ON(__alignof(*save_area) < 64);
+    save_area = _xzalloc(xsave_cntxt_size, __alignof(*save_area));
     if ( save_area == NULL )
         return -ENOMEM;
 

diff --git a/xen/include/asm-x86/xstate.h b/xen/include/asm-x86/xstate.h
index 12d939bd2407b6571afd22c6d63173a0d04f7a0f..c902bb1c4c4d5a60f4944aacf419f6f877a8c675 100644 (file)
--- a/xen/include/asm-x86/xstate.h
+++ b/xen/include/asm-x86/xstate.h
@@ -48,9 +48,9 @@ extern u64 xfeature_mask;
 extern unsigned int *xstate_sizes;
 
 /* extended state save area */
-struct __packed __attribute__((aligned (64))) xsave_struct
+struct __attribute__((aligned (64))) xsave_struct
 {
-    union {                                  /* FPU/MMX, SSE */
+    union __attribute__((aligned(16))) {     /* FPU/MMX, SSE */
         char x[512];
         struct {
             uint16_t fcw;